In 1960, Zenith produced a limited quantity of speaker boxes called the Converta (Royal 55C) to go with the Royal 50. It’s purpose was to convert the shirt pocket sized radio into a table radio that produced a bigger sound through it’s 4″ speaker.
It measures 6″ high, 7.5″ wide, and 3″ deep and weighs only 18 ounces. It works well, producing a “bigger” sound, but with the radio installed, it becomes quite top-heavy and not very stable and with a fall or two, the thin legs would break, making it even less stable. It’s cost was $39.95 – $44.95 which included the radio (I have a 1962 price guide that quotes these speaker boxes were a $10 option). Not a hot seller. They are made of brittle plastic and as a result, these are very difficult to find today in good condition.